Lapping "High end" scope rings?

[IdahoBeav]

I'm doing no such thing- and in fact, it's this inane "i never lapped muh rings, never had no problems with it" mentality that is the appeal to tradition.

Yes, by referencing the process of some "top builders", you are appealing to authority and tradition. There are reputable people in the precision rifle world that do not believe in lapping and bedding. However, merely mentioning their opinion is not relevant. Nonetheless, yes, the "I've never had a problem before" reasoning is also an appeal to tradition, and this is why I am asking questions about the science and the physical properties of lapping and bedding high quality rings and rails instead of merely citing a track record or the process used by others.

The only rail I trust not to bed? An integrally machined one. The difference between those who don't know this and those who do is the difference between those who buy their ammo by the case or by the box. I'm not trying to be elitist here - far from it. I'm trying to share hard-earned, very expensive and painful experience and knowledge, that makes a difference.

I'll revert back to my question about the bedding compound expanding so much that it is subjected to equal force as the areas where steel is touching. There is also the difference in hardness of steel and the compound. If you're talking about building up material and sanding it to the correct height, that would make some sense, but then you're pretty much right back to trying to redo what was done by CNC at the factory. At best, you're using an imprint of a bead blasted receiver and the limited precision of hand tool work. This very well may be more accurate than the manufacturing process of cheap parts, but I am not convinced that the same is true for high quality parts.

Would you not take 15 minutes to check the air in your tires before a long trip, or hauling a load? It's a 1 time thing.

Ok, you're talking about my opinion and experience now, so it's nothing more than that, but no, I would not check my tire pressure if it required removing material from the treads.

By torqueing the rail and rings to the rail, placing the scope in the rings, finger tightening the rings to the scope, and ensuring the scope slides and twists freely, I feel I can be sure that the rings pass the QC/QA. I can set the scope, torque the rings to spec, and be good to go, and then if/when the scope is removed later, there is no damage to the scope. Again, this is just my opinion and experience.

As for a scientific answer, I am asking to be convinced that smearing JB weld and abrasive grease and using a $100 Chinese tool by hand corrects an issue that is left over from advanced CNC work in a factory.

 

[RockAndSage]

That doesn't answer the question. You are truing for a specific rifle, correct? How does that impact things for when you move the scope and rings together to a different rifle?

Don't move the rings and scope together to a different rifle. Apologies if it wasn't clear with what I wrote.

Yes, when you true rings on a rifle, they're properly trued to that rifle and that rifle alone, in that exact spot on that exact rifle with that exact torque - just consider them a part of that gun and let it go with the security of a properly done job.

Take them off, they're not trued. Move them forward or back, they're not trued. Put them on another gun, they're not trued. The degree of that change absolutely depends on the new rifle and its base, but it's not advisable to treat them like they're interchangeable, unless you want to re-lap them. I've never done that, and don't know how many times you could do that before too much material is missing to get a snug fit on that scope. But unless you're in some sort of weird emergency, true 1 set of rings to a rifle and just consider that a part of that specific rifle and move on if you need to swap its scope to another rifle.

 

[RockAndSage]

Yes, by referencing the process of some "top builders", you are appealing to authority and tradition. There are reputable people in the precision rifle world that do not believe in lapping and bedding. However, merely mentioning their opinion is not relevant. Nonetheless, yes, the "I've never had a problem before" reasoning is also an appeal to tradition, and this is why I am asking questions about the science and the physical properties of lapping and bedding high quality rings and rails instead of merely citing a track record or the process used by others.

I'll revert back to my question about the bedding compound expanding so much that it is subjected to equal force as the areas where steel is touching. There is also the difference in hardness of steel and the compound. If you're talking about building up material and sanding it to the correct height, that would make some sense, but then you're pretty much right back to trying to redo what was done by CNC at the factory. At best, you're using an imprint of a bead blasted receiver and the limited precision of hand tool work. This very well may be more accurate than the manufacturing process of cheap parts, but I am not convinced that the same is true for high quality parts.


Ok, you're talking about my opinion and experience now, so it's nothing more than that, but no, I would not check my tire pressure if it required removing material from the treads.

By torqueing the rail and rings to the rail, placing the scope in the rings, finger tightening the rings to the scope, and ensuring the scope slides and twists freely, I feel I can be sure that the rings pass the QC/QA. I can set the scope, torque the rings to spec, and be good to go, and then if/when the scope is removed later, there is no damage to the scope. Again, this is just my opinion and experience.

As for a scientific answer, I am asking to be convinced that smearing JB weld and abrasive grease and using a $100 Chinese tool by hand corrects an issue that is left over from advanced CNC work in a factory.

Sure.

 

[sndmn11]

Don't move the rings and scope together to a different rifle. Apologies if it wasn't clear with what I wrote.

Yes, when you true rings on a rifle, they're properly trued to that rifle and that rifle alone, in that exact spot on that exact rifle with that exact torque - just consider them a part of that gun and let it go with the security of a property done job.

Take them off, they're not trued. Move them forward or back, they're not trued. Put them on another gun, they're not trued. The degree of that change absolutely depends on the new rifle and its base, but it's not advisable to treat them like they're interchangeable, unless you want to re-lap them. I've never done that, and don't know how many times you could do that before too much material is missing to get a snug fit on that scope. But unless you're in some sort of weird emergency, true 1 set of rings to a rifle and just consider that a part of that specific rifle and move on if you need to swap its scope to another rifle.

That makes good sense, thank you.

It sounds like for someone like me and my wife, lapping is likely a negative since we move scopes around rifles regularly.

 

[RockAndSage]

That makes good sense, thank you.

It sounds like for someone like me and my wife, lapping is likely a negative since we move scopes around rifles regularly.

Happy to share what I've learned. Keep in mind that "out of true" is always a matter of degree, and how much that matters also depends on the scopes you're using, and how carefully you torque the rings onto the scope.

If you're swapping scopes around because you've got a limited amount of cash you can put into optics, I've definitely been there - and protecting that scope was necessarily a part of protecting what I did with my cash. Extra rings are cheaper than a new scope. As a general rule, the lighter or cheaper the scope, the more this issue of ring alignment matters. It didn't matter as much, decades ago, when scopes were made of steel or had thicker walls. And unfortunately, people's norms and expectations about mounting a scope were broadly set during that time, and we stumble into these problems without realizing they were there. Modern, higher quality scopes that are heavier, especially ones with 34mm tubes, tend to have thicker walls and are less prone to the kind of problematic deformation that can come from rings being out of true, or those rings being over-torqued.

But if you want to protect the scopes you've invested in, well...if I personally were required to only have 1 scope, and needed to use it across different rifles...then each gun gets its own set of rings, lapped in place, and they're just considered part of that gun after that. That would probably be the safest way to use 1 scope across multiple guns.

 

[SDHNTR]

Yes, by referencing the process of some "top builders", you are appealing to authority and tradition. There are reputable people in the precision rifle world that do not believe in lapping and bedding. However, merely mentioning their opinion is not relevant. Nonetheless, yes, the "I've never had a problem before" reasoning is also an appeal to tradition, and this is why I am asking questions about the science and the physical properties of lapping and bedding high quality rings and rails instead of merely citing a track record or the process used by others.

I'll revert back to my question about the bedding compound expanding so much that it is subjected to equal force as the areas where steel is touching. There is also the difference in hardness of steel and the compound. If you're talking about building up material and sanding it to the correct height, that would make some sense, but then you're pretty much right back to trying to redo what was done by CNC at the factory. At best, you're using an imprint of a bead blasted receiver and the limited precision of hand tool work. This very well may be more accurate than the manufacturing process of cheap parts, but I am not convinced that the same is true for high quality parts.


Ok, you're talking about my opinion and experience now, so it's nothing more than that, but no, I would not check my tire pressure if it required removing material from the treads.

By torqueing the rail and rings to the rail, placing the scope in the rings, finger tightening the rings to the scope, and ensuring the scope slides and twists freely, I feel I can be sure that the rings pass the QC/QA. I can set the scope, torque the rings to spec, and be good to go, and then if/when the scope is removed later, there is no damage to the scope. Again, this is just my opinion and experience.

As for a scientific answer, I am asking to be convinced that smearing JB weld and abrasive grease and using a $100 Chinese tool by hand corrects an issue that is left over from advanced CNC work in a factory.

He’s talking about checking, not needlessly lapping unless warranted.

And I think you are giving most rifle manufacturers too much credit. If you did take the time to check with a lapping bar, you’d find true receivers are 50-50 at best

 

[sndmn11]

As already pointed out, one would leave the rings with the rifle and simply swap scopes without disturbing the bottom halves of the rings.

You are correct to think that lapping rings into alignment on one rifle might make the misalignment worse on another gun.

I am genuinely surprised you pic rings as regularly as you've said. To me the advantage of a pic system is being able to have infinite interchangeability. Right now we have three more scopes than rifles, and one more set of rings than scopes. I can determine a poi issue within a half an hour or much less by having a scope/ring set ready to go. Three times in the last year I've been at the gun club with people cussing their results, and with a few minutes we figured out there was an issue with their scope or rings. Thankfully all had pic rails so my unlapped beater scope and rings worked.

I see the potential value in a ring set that stays permanently on the rifle, but on any pic ring you loose the utility of the system.

 

[gbflyer]

RockandSage is 100% on. Argue with him all you want, it’s your bent scope.

 

[E.Shell]

I am genuinely surprised you pic rings as regularly as you've said. To me the advantage of a pic system is being able to have infinite interchangeability. Right now we have three more scopes than rifles, and one more set of rings than scopes. I can determine a poi issue within a half an hour or much less by having a scope/ring set ready to go. Three times in the last year I've been at the gun club with people cussing their results, and with a few minutes we figured out there was an issue with their scope or rings. Thankfully all had pic rails so my unlapped beater scope and rings worked.

I see the potential value in a ring set that stays permanently on the rifle, but on any pic ring you loose the utility of the system.

Different shooters have varying requirements.

Almost everything I worked on had been brought to a long range precision rifle class by competitors and tactical marksmen. The scopes typically stayed with the rifles.

While your point about interchangeability is valid and well made, interchangeability often has a price. We see this in gun parts intended to be changed out without fitting (like AR-15 parts kits) and the inconsistent performance inherent to certain platforms.

That so many people swap scopes around and don't pay attention to ring contact quality and ring axis alignment is evidenced by the huge number of used scopes being sold with "minor ring marks" (damaged by the installer).

If a additional scopes are desired for a certain rifle, there is no problem with lapping a set of rings with each scope that would be mated to that particular rifle/base and easily interchanged with no ill effects.

If one scope is to service several rifles, or is to be used as a troubleshooting tool, we could forego lapping and simply take the probable scope tube damage as the price to be paid for this interchangeability.

 

[IdahoBeav]

The alert for this reply came in way late for some reason, and I missed this comment, but thank you for writing out this information.

As pointed out by other posters, the rings themselves, and degree of their precision, is not usually the reason to lap. The reason is the composite error of all mounting parts combined/added and their effect on ring axis alignment.

Rings of lesser precision also benefit from lapping by having sharp edges and high spots corrected.

So then, with a high quality rail & ring setup, the deflection is going to come from the receiver not matching the straight rail, and when the rail is torqued, it twists, therefore causing the rings to be out of alignment ever so slightly?

I do agree that with cheap rings, the sanding is important, but on rings like Nightforce, the inside surface is completely smooth.

Lapping bars are merely round rod stock that slides between the loosely clamped rings. The diameter of the lapping bar is typically a few thousandths of an inch less that the corresponding scope tube diameter, in order that we do not loosen the fit if done properly.

It's machined round stock, right? So is there reason to assume that it is machined with greater accuracy than the scope tube? Do the bars sand out imperfections that are not caught by a free moving scope in finger-tightened and mounted rings?

Epoxy expansion does not affect this process, nor contribute to tightening the screws. Bedding the base normally helps with keeping the ring bores aligned and reduces the need to lap, but there are often sharp edges and/or high spots and lapping will address these.

So, you're filling in the gaps of imperfection between the receiver and rail? And you're finger tightening so the rail remains un-deformed by the torque of the screws to the receiver? So then, the hardened filler material will not be to the exact elevations or surface to perfectly fit the imperfect receiver (that would require adding excessive material and machining down to size?) , but it will be better than before. The compound will occupy most of the gap space under tension?

This may be the source of your questions...the ring screws are NOT tightened down onto the lapping bar with any substantial force and certainly not clamped onto the bar or brought up to torque.

But there is a little tension, enough to slide the bar while still applying enough pressure for the abrasive grease to cut. Is the shape and touching surface area of the ring different between slightly tightened on the bar vs torqued to spec on the scope? Maybe this discrepancy is negligible?

I agree that this is all important on cheap mounts, and 2-piece mounts add more probability, but how often is it that you see a receiver so bad that it twists the pic rail enough to cause misalignment, and have you seen misalignment on a high quality rail and set of rings where the scope goes in and out of the mounted ring bottoms with ease, and the scope slides and spins easily with the rings finger tightened?

 

[E.Shell]

The alert for this reply came in way late for some reason, and I missed this comment, but thank you for writing out this information.

My fault. It came in late because I am new and this is one of my first posts here at Rokslide. My post was delayed for moderation and thus did not immediately show up on the thread or in your alerts.

So then, with a high quality rail & ring setup, the deflection is going to come from the receiver not matching the straight rail, and when the rail is torqued, it twists, therefore causing the rings to be out of alignment ever so slightly?

Two parts to this...

Where I used the term "deflection" above, it was in the context of the ring material moving away from cutter pressure where it is thin (thinnest) on the sides. While cutting on a mill, the cutting tool presses against the material and knocks chips off of it like a bunch of little chisels in rapid series. Sharper tools cut with less pressure, so deflection is minimized. When the cutter pressure is removed, the material springs back, and in the case of scope rings, the sides of the ring bore close up slightly. I have seen this to a greater or lesser degree with almost all ring manufacturers I have worked with; Badgers, Farrells, Seekins, NightForce, Leupold, Weavers, Millets...

The second part of the deflection discussion is that yes, the top of most rifle receivers are not perfectly true and the base will move to meet the receiver surfaces as the screws are torqued. If the rail is no longer flat, the rings, no matter how precisely made, cannot be axially aligned due to being moved to a different plane and due to being twisted by the base that was forced (deflected) out of alignment.

For example, Remington M700 receivers are "centerless ground" and "completely wild" is the way I would describe the precision of the top surface, not to mention screw hole (mis)alignment vs the barrel bore axis and vs each other. I have seen Remingtons and others require 0.005" or more in shims to prevent movement when torquing the screws. Enough that I keep shim stock in stock. Enough that custom gunsmiths commonly re-bore the #6 base screw holes on a mill to #8 so they can be properly aligned with the bolt bore and barrel thread axis.

Note that we can always ignore the base distortion, ring alignment and internal ring finish, still go hunting and nothing bad may ever happen. The scope can be sold later with "minor ring marks".

I do agree that with cheap rings, the sanding is important, but on rings like Nightforce, the inside surface is completely smooth.

Many are, some aren't. The inner surfaces of the ring bore are typically smooth, but very slight burrs can be raised at the edge of the bore, which can be very sharp. One spot that seems to be a constant is the top/bottom edge of the ring bore, where we experience machining deflection as discussed above. I have seen scopes scratched just laying them into the bottom rings.

As a sidebar, "sanding" implies an aggressive approach and a lot of material being displaced. I realize you may not mean it that way. Correct lapping is more of a polishing/honing action and ring lapping compound is very fine, perhaps #600/800 grit and is not to be confused with automotive valve lapping/grinding compounds, which are often as coarse as #80/100/150/200/240. Entirely different animal.

It's machined round stock, right? So is there reason to assume that it is machined with greater accuracy than the scope tube?

Yes, machined bar stock. No, no reason to assume it is more precise in diameter or concentricity (roundness) than a well made scope tube. It is a tool, not a gauge or standard.

The bar is turned on a lathe and therefore reasonably round. I have a 1" bar, a 30mm bar and a 34mm bar and none of these exhibit differences in diameter along their length, which would be noticeable by being tighter and looser as those spots pass between the rings.

In technique, the bar is moved laterally as we stroke it forward and aft. It is also rotated slightly as it moves. This combination movement serves to keep the ring bores round and aligned. If pressure is kept on the fore/aft direction, the ring bores will remain round.

The diameter of the bar is a few thousandths under the nominal size and does not wallow out the ring bore.

The bar serves the purpose as a tool and meets the necessary standard for precision.

I feel compelled to note that we are *polishing* surfaces and while it is indeed possible to remove a lot of metal using a lapping bar, that is neither desirable nor done accidentally.

Do the bars sand out imperfections that are not caught by a free moving scope in finger-tightened and mounted rings?

Possibly. Once ring screws are driven to full torque, imperfections previously not apparent can be telegraphed into the scope tube and/or finish.

I would agree that if the scope tube moves smoothly under the conditions stated, it would rule out most interior imperfections. The caveat is that until the rings are torqued, 'finger tight' would not show a potential misalignment bind due to being what we would be tightening against. The misalignment bind would prevent full travel of the rings and make us think we were honestly finger tight.

So, you're filling in the gaps of imperfection between the receiver and rail? And you're finger tightening so the rail remains un-deformed by the torque of the screws to the receiver?

This is correct.

So then, the hardened filler material will not be to the exact elevations or surface to perfectly fit the imperfect receiver (that would require adding excessive material and machining down to size?) , but it will be better than before. The compound will occupy most of the gap space under tension?

No, the epoxy would completely fill any voids and would be both in contact with the rifle receiver and with the bottom of the rail, thus preventing deflection as the screws are eventually tightened down to specified torque values after curing.

When bedding the rail, it is dry-fitted first and one notes where the rail fails to meet the receiver. When the epoxy is added, those screws are not tightened as much as those that make good contact, thus helping to maintain good alignment to the receiver and avoid distorting the rail.

Bedding the rail really IS the most desirable first step, because it helps minimize bending the rail to conform to the receiver. In an ideal world, one would always do this first, but the world is not always ideal.

The problem I had when giving classes and providing scope installation is 'time'. There is not time during a three-day precision rifle class to bed a rail and let it cure to sufficient/final hardness. With new students (the ones that needed scope mounting/correction), we did one class/shop day and two field days. My answer to that was to shim the receiver x base to allow the base to lie flat and tight. As mentioned above, I keep various thicknesses of shim stock on hand. I have a punch/die set to make the screw holes cleanly and correctly. I will shim the base until there is zero movement, torque the screws to spec, then mount and lap the rings as described above.

But there is a little tension, enough to slide the bar while still applying enough pressure for the abrasive grease to cut.

This is correct.

Is the shape and touching surface area of the ring different between slightly tightened on the bar vs torqued to spec on the scope? Maybe this discrepancy is negligible?

Once the lapping begins, we would lap a few strokes, then ensure the ring screws are evenly tensioned. We "chase" the bar down as the lapping compound is exhausted and as we remove burrs and high spots that prevent fully seating the bar/scope tube. The final difference in fit would be half the difference between the bar diameter and scope tube diameter...negligable.

I agree that this is all important on cheap mounts, and 2-piece mounts add more probability, but how often is it that you see a receiver so bad that it twists the pic rail enough to cause misalignment...

Almost always. Enough that when I DO see a rail lie perfectly tight and flat against the receiver, I say "Holy **** you guys, look at THIS!! I'm buying a lottery ticket tonight!".

... and have you seen misalignment on a high quality rail and set of rings where the scope goes in and out of the mounted ring bottoms with ease, and the scope slides and spins easily with the rings finger tightened?

The rail and rings are easy to make precisely enough on a 'stand alone' basis. Once the rifle is introduced and all the tiny errors added up, usually it all goes out the window.

In direct answer to your question, I don't know. I have seen so many issues with rifles, bases and rings, I would never dare slide a client's scope around in the rings and would be embarrassed to scratch one of my own scopes like that.

 

[RockAndSage]

As pointed out by other posters, the rings themselves, and degree of their precision, is not usually the reason to lap. The reason is the composite error of all mounting parts combined/added and their effect on ring axis alignment.

Rings of lesser precision also benefit from lapping by having sharp edges and high spots corrected.

One thing you will notice as a recurring pattern when lapping is that while the rings are machined, the thinner areas at the sides tend to deflect away from the cutter. After the cutter is retracted, that area of the rings spring back. Anyone familiar with metal machining has seen this deflection. Sharper tools deflect less, but some deflection is almost always evident. When the rings are lapped, this area is corrected and no longer grabs the scope as the scope tube enters the rings.

Lapping bars are merely round rod stock that slides between the loosely clamped rings. The diameter of the lapping bar is typically a few thousandths of an inch less that the corresponding scope tube diameter, in order that we do not loosen the fit if done properly..

We are only ensuring alignment of the ring axes, not re-cutting the bores.

This is all about being kind to the scope. The scope tube, unless junk or damaged, can be assumed to be straight and cylindrical and we are using the lapping method to ensure it lies in alignment to the ring bores.

When bedding bases, the standard practice is to lightly tighten the base screws just enough to press the base down onto the bedding compound, not squeeze the material out. Once the compound is cured, the screws are brought up to the specified torque value and nothing moves during that process.

Epoxy expansion does not affect this process, nor contribute to tightening the screws. Bedding the base normally helps with keeping the ring bores aligned and reduces the need to lap, but there are often sharp edges and/or high spots and lapping will address these.

This may be the source of your questions...the ring screws are NOT tightened down onto the lapping bar with any substantial force and certainly not clamped onto the bar or brought up to torque.

When I was teaching long range precision, I usually helped students with installing their scopes. Most people really don't know how to properly mount a scope and I usually saw both eye relief errors and almost always out of level. I used a Starrett 4" machinist's level to correctly level long range scopes.

I have mounted several hundred tactical/precision scopes in the following manner:

Picatinny style mounts:
The rings are set loosely onto the base, pressed forward against the face of the slot and the clamp screws lightly tightened.
The lapping bar laid onto the bottom ring halves and first used as an alignment tool.
The ring caps are lightly snugged up on the bar to align them to each other as closely as possible.
The ring clamp screws are then torqued to the base. You will not touch these clamp screws again.
The ring caps are removed.
The lapping bar is removed, loaded with lapping compound and set back into the bottom ring halves, now to be used as a lapping tool.
The ring caps are placed back on and the cap screws lightly snugged.
The bar is then slid back and forth inside the rings, using a push/pull motion with light rotation.
As the compound is exhausted and the rough/high spots worn down, chase the bar down by lightly tightening down the cap screws. At no time during lapping will the ring screws be "tight".
You will be able to feel when the lapping compound is completely exhausted and stops cutting, and you will stop at that time. One cycle is usually enough to take care of the worse of it.

Remove and clean the ring caps and lapping bar. Keep the respective ring cap both matched to the ring bottom and oriented the same. I usually index mine and students with a very small prick punch where the rings meet - one dot at the front, two dots at the back.
Clean the ring bottoms.
Inspect the condition of the ring contact surfaces. You will be able to see finish wear where material was removed. I usually go for about 50-75% contact. I do not completely remove the interior finish. Note at this time that the areas touched by the lapping bar were the high spots and pressure points against your expensive scope tube.

Once you have 50% or so contact, make sure everything is clean, loosely install the scope and ring caps, level your scope, set your eye relief and torque your ring cap screws.

Torque values are designed to deform (stretch) the screw just enough that it will return to its original shape when pressure is released. You are correct and yes, this DOES weaken the screws more and more each time, ** IF** we actually torqued them down onto the lapping bar, which we DO NOT.

If you would:
a) like to have your scope work as smoothly (magnification and parallax adjustments) as designed, and
b) like to have the best stability via increased/improved tube/ring contact, and
c) wish to eventually resell your scope without ring damage ("ring marks"), then
it's NOT "chasing dust" and *proper* lapping is a good idea.

If one doesn't care about any of that, one shouldn't bother with lapping, but also shouldn't object to those that do.

^^^ This ^^^ ....mostly. In most cases, we will still see a slight out-of-round condition due to cutter deflection.

Look at this process as matching the rings to a particular rifle/base platform.

As already pointed out, one would leave the rings with the rifle and simply swap scopes without disturbing the bottom halves of the rings.

You are correct to think that lapping rings into alignment on one rifle might make the misalignment worse on another gun.

@E.Shell , I missed this post yesterday entirely, somehow. It's excellent, and I learned several distinctly new points. Thank you for the time and effort you put into sharing all of it, it's genuinely appreciated.

 

[Blacktail247]

Today I bedded a rail to a rifle and this is how far things were misaligned with the rear screws just snug. Seems like a lot to me. That’s a 308 case, it was just something laying there for reference. With a straight edge across the top the rail it looked true and I was bedding any way so I just went for it. Had I just torqued it down it would have threw off ring alignment if they were even true to begin with.